The subject matter disclosed herein relates to combined cycle power plants and, more particularly, to a method of increasing power output from a combined cycle power plant during select operating periods.
Many combined cycle plants today include power augmentation supplied by supplementary firing from a heat recovery steam generator (HRSG). The supplementary firing is done either ahead of or within the HRSG to achieve additional steam production to increase an overall plant power output to a power grid. The HRSG supplementary firing is most frequently utilized to provide a significant amount of output increase during peak operating periods, such as on hot summer days, during which gas turbine power is down and electricity demand is high. The amount of the power augmentation is limited by a number of equipment limits, such as, a steam turbine throttle pressure (high pressure turbine inlet pressure) limit, HRSG duct burner exit temperature limit, steam turbine exhaust pressure limit and the like. In addition to equipment limits, power augmentation is also constrained by an environmental permit issued to the power plant. Once any of the equipment limits and/or environmental limits is reached, the combined cycle power plant can no longer increase power output. As a result, brown-outs and/or black-outs are possible if the power demand exceeds the maximum power that the combined cycle power plant can deliver.